Ricerc@Sapienza

Rock-burst is a local instability problem affecting compact rock-masses in deep tunnels: it can generate important over-breaks, but even more, safety issues for workers in the area where it occurs. The experimental study, aimed at predicting rock-burst occurrence during the excavation of the Brenner Base Tunnel, was carried out in massive granite below an overburden of 1000-1200 m.

The paper describes the experience gained during the excavation of some stretches of the Brenner Base Tunnel system, a complex underground network for the connection of the city of Fortezza, in Italy, to the city of Innsbruck, in Austria, in the framework of the Scandinavian Mediterranean corridor 5 of the Trans European Network-Transport.

This paper deals with the analysis of overbreak in tunnels excavated with the drill-and-blast method. The overbreak phenomenon has many negative impacts on tunnelling organisation and economy and its precise assessment plays a fundamental role in the process of construction optimisation. The study proposes an operative methodology to estimate overbreak volumes and to distinguish so-called technical overbreak, mainly related to drill-and-blast design and execution, from geological overbreak, typically influenced by rock-mass characteristics.

Risk associated to rock-burst occurrence in tunnels is nowadays managed by a continuous monitoring of acoustic emissions recorded during the excavation, whose characteristics depend on the failure processes ongoing in the rock-mass. A new in situ test was specifically designed with the aim of calibrating the alarm threshold for rock-burst occurrence. The test consists in compressing to failure a portion of the rock-mass at the tunnel side-wall by means of a couple of flat-jacks, measuring simultaneously the generated acoustic emissions with accelerometers.